The Solar Electric Power Association (SEPA) has named the top 10 U.S. electric utilities that added the most new solar power to their systems and most solar on a watts-per-customer basis in 2013. The list is part of the seventh annual Utility Solar Rankings report, which SEPA will release in June.

The organization says the utilities that made the cut in the total MW ranking accounted for 82% of all solar capacity integrated last year, up from 73% in 2012. SEPA adds that the top three leading implementers of utility solar in the MW list hail from the western half of the U.S. - Pacific Gas and Electric Co. (PG&E), San Diego Gas and Electric Co. (SDG&E) and Arizona Public Service (APS).

This is the sixth year that PG&E has topped the list, SEPA notes. In addition, six of the 10 utilities previously ranked in 2012, and newcomers to the list include Duke Energy Progress, National Grid and Georgia Power.

According to SEPA, the watts-per-customer ranking takes into account the number of customers each utility serves relative to its solar MW installed, giving small utilities a means to measure the relative intensity of their solar energy capacity on an equal footing with any other utility, regardless of size.

Sterling Municipal Light Department (SMLD), a public power utility in Massachusetts that serves 3,700 customers, tops the watts-per-customer list. SDG&E and Silicon Valley Power round out the top three. The Hawaiian utilities and Imperial Irrigation District (IID) made the ranking in 2012.

Months after the U.S. Environmental Protection Agency released its Clean Power Plan, which will create new regulations for existing power plants, the agency says it has received loads of feedback to consider.